It is known to provide a baking oven, dryer or other gas treating apparatus in which the heating or drying air or gas is emitted through a series of gas distribution box nozzles positioned in succession along the path of travel of the goods being baked or web of material or layer of granular material to be dried or treated, each nozzle extending laterally across the goods or material. As such distribution boxes and nozzles are lengthened to accommodate ever greater and greater widths of gas treating apparatus, uniformity of treatment across the goods, web or layer of granular material becomes more and more difficult. The reason for this is that the treating air or gas normally has to be fed to each distribution box from one side of the gas treating apparatus. This means that the air or gas flowing from the distribution box nozzle may have a higher velocity adjacent the inlet side, or the opposite side depending upon the length of the box. Even if the distribution box is fed from the center of the apparatus, which may be awkward, the velocity of the flow from the distribution box nozzle varies being higher in the center of the nozzle. The result is that with conventional gas distribution boxes, the treatment or drying of the material being treated or dried is non-uniform.
In addition, particularly where the distribution box is fed from one side of the dryer or gas treating apparatus, the gas flow has a direction of movement away from the box inlet end and towards the exhaust side of the dryer. In the case of drying of carpeting and other such material, this tends to flatten the upstanding carpet tufts impeding the drying. In the case of granular material, it causes at least some of the granular material to shift to the exhaust side of the dryer resulting in an uneven layer of material passing through the dryer, and uneven drying.
In prior U.S. Pat. No. 3,429,057, assigned to assignee of the present application, an improvement was shown by which drying air or other treating gas was distributed uniformly across the entire width of the area to be dried or treated. This was accomplished by employing a pair of distribution boxes which were in side-by-side relationship, one of the distribution boxes being fed from one side of the dryer or gas treating apparatus and the other distribution box from the opposite side of the dryer. The streams of drying air (in the event the treating process was drying) which flowed from the distribution box nozzles tended to have opposite horizontal directions of movement which in turn created a myriad of small vortices perpendicularly impinging against the material being dried. This prevented laying over of the carpet or flow of particulate material to one side of the dryer, and thus resulted in more uniform drying of the material being treated. With regard to velocity or volume of flow, the flow from one of the distribution boxes compensated for differences in flow from the other distribution box, with the result that the merged streams had a substantially uniform velocity of flow and volume across the width of the carpet or granular material. This also resulted in more uniformity of drying or gas treating.
The invention of said prior patent was of particular importance in the drying of heat sensitive materials such as rugs having polypropylene backings wherein excessive temperatures (due to greater air flow) could melt the backing. The balancing of flows by the process of the prior invention enabled obtaining uniformities of air temperatures in dryers unknown prior to such invention.
The disclosure of prior U.S. Pat. No. 3,429,057 is incorporated by reference herein.